At present there is known in the art a multitude of refractory suspensions adapted for making graphite lost wax moulds for casting, e.g., titanium pieces.
The process of making said foundry moulds is conducted by dipping wax patterns into a prepared suspension which is followed by dusting a graphite powder thereon. On applying each next layer to said wax pattern it is dried at a temperature of 28.degree.-30.degree. C. for 2.5 hours. The pattern is thus coated with 7-8 layers of graphite whereupon the wax is melted out in a steam bath. The moulds released from the wax patterns are subjected to curing by heating them to a temperature varying in the range between 1300.degree. and 1350.degree. C. and holding at this temperature for 4 hours.
The baked moulds are placed in a vacuum skull furnace and filled with molten metal. The thus produced castings are discharged from the furnace and released from the moulds whereupon they are cut off the gate system and heads. All these operations completed the castings are subjected to sandblasting.
For example there is known in the art a graphite-resin suspension comprising a filler--a graphite powder, a binder-phenol-formaldehyde resin, hydrochloric acid and an esteraldehyde fraction, the ratio of said suspension constituents being respectively as follows (parts by weight): 37-44; 35-37; 3-4; 18-22.
The disadvantage of said suspension resides in that in making moulds thereof use is made of a graphite powder as a filler, which enhances the heat conductivity of said moulds, a feature adversely affecting the mould-filling ability when producing thin-section parts and giving rise to cold shuts that are liable to appear on the surface of said castings. Moreover the moulds made on the basis of said suspension cannot be reclaimed insofar as the recurrent use of the powders obtained by comminuting used moulds causes a greater scatter in the mould geometric dimensions with the ensuing deterioration of casting accuracy.
There is likewise known in the art a refractory suspension for making casting moulds comprising the below-listed constituents taken in the following amounts (percent by weight):
a filler--a graphite powder which is the basic component of said suspension, and metallic powdered titanium, 0.8-2.5; PA0 a binder--phenol baryta resin, 20-25; PA0 a hardener--a mixture of sulphonaphtenic acids, the so-called "Petrov's contact catalyst", 7-9; PA0 an organic solvent--alcohol, 30-36.
The disadvantage peculiar to said suspension lies in a higher collapsibility of the moulds produced thereof, which is also liable to cause casting rejects. The use of a graphite powder as a filler enhances the heat conductivity of the moulds decreasing thereby their filling ability which is of paramount importance in casting thin-section pieces with a wall thickness of 1.5 mm and up to 30 mm long which is actually impractical in said mould. The moulds produced from said suspension are almost unsuitable for reclamation, the reclaimed powders not allowing precision castings to be produced therein.
It is an object of the present invention to overcome the above disadvantages.
The principal object of the invention is to provide a refractory suspension whose application for making foundry moulds would make it possible to enhance the geometric accuracy of cast pieces.
Another object of the invention is the provision of a refractory suspension which would allow enhancing the mechanical strength of the foundry moulds produced on the basis of said suspension.
Still another object of the invention is the provision of a refractory suspension whose application for making foundry moulds would make it possible to obtain cast pieces with thinner sections and a higher surface finish.
Yet another object of the invention is to provide a refractory suspension for making foundry moulds which would enable shell moulds to be recurrently reclaimed after filling them with metal without impairing the quality of the moulds produced of said reclaimed powder.